Gas generating electric discharge device



June 8, 1965 J. D. COBINE GAS GENERATING ELECTRIC DISCHARGE DEVICE FiledMay 10, 1961 E F/g.

j, 22 U 6 2/ x 7 l I, /3 2 2 1 0 22 22 Pulse Source lnvemar: James D.Cob/he His Aflorney.

United States Patent The present invention relates to electric dischargedevices adapted toswitch high voltages and currents with speed andprecision, and more particularly to such apparatus in which switching isaccomplished by triggering electric breakdown between a pair of fixedelectrodes separated by agap in vacuo.

Gap. switching devices are devices normally maintained in an opencircuit condition which, when subjected to an appropriate signal, areswitched to a closed circuit condition and pass electric currenttherethrough. Such devicesfare used to great advantage as overloadprotectors,

lighting arresters and for the precision switching of ex tremely highvoltages and currents, as for example, in discharging capacitor banks toobtain a very short pulse of extremely high current.

For these uses, gap discharge devices must be able to withstand highvoltages and to break down or fire only when desired. They must beadapted, for many applications, tdfrepeatedly fire, often thousands oftimes, in response to essentially the same breakdown conditions, withthe same firing time. In other applications, as for example, when usedas lightning arresters, it is imperative that such gap devices have anextremely short recovery time so as to be ready to function again ashort time after firing; i

Most prior art gap discharge devices are charged with agaseousatmosphere, often at super-atmospheric pressure. Althoughsuitable for many applications, gaseous gap discharge devices usuallyhave long recovery times, due to the necessity of ionized gases thereinbecoming deionized before full recovery is effected. Additionally, sincethe hold-oifvoltage of a gap discharge device is dependent upon thedielectric strength of the gas therein, gaseous gaps .areoften quitelarge when designed for use at high voltages.

Perhaps the greatest disadvantage of scaled gaseous gap dischargedevices, however, is. due to the fact that with use, gasis removed orcleaned-up from the device by entrapment with deposited metallicparticles which are sputtered from the electrodes of the gap. Thiscleanup? changes the characteristic of the gap so that it does notperform reproducibly and the device must often be replaced long beforeactual failure.

Vacuum gap discharge devices have been proposed as a means to overcomemany of these disadvantages. In theory, a vacuum gap dischargedevicewould be smaller, due to the high dielectric strength of a vacuum;its recovery time would be much shorter; and, since there is no gas tobe removed by sputtered metallic particles, a vacuum gap should notchange its operating characterisitcs. In

practice, however, prior art vacuum gap discharge devices have notproven to be reliable, either .as to firing voltage, hold-off strength,or recovery time. In prior art vacuum spark gap devices, the operatingcharacteristics seem, to be a function of the devices past history, suchas the time lapsed since last firing.

It is a general object of thepresent invention to provide gap dischargedevices which overcome one or more of the foregoing disadvantages.

A more specific advantage of the invention is to provide triggered gapdischarge devices adapted to reproducibly fire at preselected voltageconditions, and to rapidlyrecover to the prefiring condition.-

Another object of the present invention is. to provide triggered gapdischarge devices with reproducibly short firing times.

A further object of the invention is to provide improved gap dischargedevices having stable, reproducible holdolf voltages, firing times andrecovery times and including dielectric trigger electrodes.

Still another object of the present invention is to provide improvedtriggered gap discharge devices which are reliable in operation andwhich may be readily and inexpensively manufactured.

The novel features believed characteristic of the present invention areset forth in the appended claims. The invention itself together withfurther objects and advantages thereof may best be appreciated byreferring to the following description taken in connection with thedrawing in which:

FIG. 1 is a vertical cross-sectional view of a triggered vacuum gapdischarge device constructedin accord with the present invention, and

HG. 2 is an alternative embodiment of theinvention in verticalcross-sectional view.

In PEG. 1, a triggered vacuum gap device includes an evacuable envelope,represented generally as 1, including an insulating cylindrical sideWall member 2 and apertured metallic disc-shaped end wall members 3 and4 spaced at opposing ends of cylindrical member 2 and hermeticallysealed thereto by suitable annular flange members. A first electrode 5and a second electrode 6 are suspended Within envelope 1' inspaced-apart relation to define a breakdown gap 7. Second electrode 6 issuspended upon electrode support member 8 which is -passed through theaperture in end wall member 3 and hermeti cally sealed thereto by meansof annular flange 9. Support member 8 terminates in a threaded stud 10for connection to an electrical circuit. Elect-rode 5 passes through theaperture in end Wall 4 and is hermetically sealed thereto by means ofannular flanges 11 and 12. Electrode 5 is a hollow cylindrical memberwith a nearly close-d end having an aperture 13 therein. The interiorhollow portion of electrode 5 is shaped with a recessed region .14 atthe upper portion thereof upon which rests a C-shaped dielectric triggerelectrodemember 15. Trigger electrode 15 is electrically connected tothe electrode upon which it rests on one side thereof andto a triggerelectrode leadld which passes out through a flanged end cap member 1'7Whichis hermetically sealed to the exterior portion of electrode member5 by glass-to-metal seals 18 and an annular flange member 19. A threadedstud 2i? is integrally connected with the protruding end of electrode 5for connection to the electrical circuit to be switched or protected. Acylindrical metallic shield member 2 1 is interspaced between breakdowngap 7 and the walls of cylindrical sidewall member Zto protect thelatter I from becoming covered with metal evolved from electrodes 5 and6 when an electric arc is established there-. betweenso as to maintainthe insulating characteristics of cylindrical member 2. Shield 21 issupported in place by springs 22 whichride upon beads 23 upon theinterior surface of wall 2. Cylindrical side wall member 2 ishermetically sealed to end Wall members 3 and 4 by suitable annularflange 24. v

Electrode 5 and electr'ode6 are preferably constructed of gas-freecopper containing less than 10- parts by weight of all non-condensablegases or non-condensable mately. amperes. or greater currents must notcause latented June 8, 1965 I aisasia the pressure within the volume, afew cycles after arcing, to rise beyond the initial value, even whenthis value is 10* mm. of mercury or less. Other metals than copper, ifsimilarly free of gases,.may be used when appropriate. The othermetallic constituents within the device may be constructed of stainlesssteel since they are not directly subjected to the high current are andare not potential sources of gas contamination.

Insulating side wall member 2 is conveniently constructed of Pyrex orVycor glass or a suitable ceramic. If glass is utilized, the flangemembers used to make hermetic seals thereto may be constructed of afernico. If, on the other hand, ceramics such as forsterite ceramics orsuch ceramics as American Lava T164 or Coors V200, are used, then themetallic parts sealed thereto should be a metal which can be used toform a good ceramic-to-metal seal, as for example, titanium. Dielectrictrigger electrode is constructed of a material having an exceedinglyhigh dielectric constant, as for example, barium titanate. Thedielectric chosen should be such that when a voltage pulse of shortduration is impressed thereupon, substantially the entire voltage isimpressed upon the C-gap thereof so as to cause the establishment of anarc thereacross. The edges of the C-gapf immediately adjacent theretoare coated with a thin film of a gas-absorbent material such as carbonor titanium and the coating is heavily impregnated with an ionizablegas, as for example, hydrogen.

In operation of the device in accord with the present invention, thehigh voltage to be switched or, if the device is to be utilized as alightning arrester, the circuit to be protected, is connected betweenthe primary electrode studs and a source of pulsed signal voltage isconnected between the first electrode stud and the trigger electrodelead 16. When a voltage pulse as low as 100 volts and of 5-10microseconds duration, for example, is applied to the trigger electrode,substantially all this voltage is impressed across the gap thereof andabreakdown is initiated. This breakdown heats the edges of the dielectricadjacent to the C-gap s-umciently to cause the evolution of gasestherefrom. By virtue of the construction of the C-gap, these gases mustnecessarily be propagated upwardly through the aperture 13 in thecathode electrode and into the breakdown gap 7. The presence of ionizedparticles within breakdown gap 7 causes breakdown of the main gapbetween first electrode 5 and second electrode 6 and the subsequentpassage of high currents therebetween.

As long as a voltage difference exists between electrode 5 and electrode6, the arc is sustained. Upon the disappearance of a potentialdifference between these electrodes, however, the arc is extinguishedand the conduction carriers therein, which consist entirely of electronsand ionized'metallic atoms evolved from the electrodes by the action ofthe arc, diffuse to shield 21, and other walls and adjacent memberswithin the envelope 1, are cooled and deionized. With the disappearanceof conduction carriers and the restoration of the high vacuum withinbreakdown gap 7, the dielectric strength of the gap increases veryrapidly, within a few microseconds, and the device is ready to functionagain.

In FIG. 2 of the drawing, there is illustrated, in verticalcross-sectional view, a vacuum gap discharge device constructed inaccord with another embodiment of the invention. The device of FIG. 2includes an envelope represented generally as and including a generallycylindrical side wall member 31 having a base portion 32 terminating ina pinch Y33 and a pair of disc-shaped end wall members 34- and 35hermetically sealed to insulating side wall member 31. A pair of primaryelectrodes 36 are disposed within envelope 30 in spaced-apart relationto define a breakdown gap 37. The electrode members are supported uponelectrode support members 38 and 39, which are passed through andhermeticaly sealed by appropriate annular flange members to end wallmembers 34 and 35 respectively. Electrode 36 and breakdown gap 37 aresurrounded by a cylindrical ferruled shield member 40 utilized toprevent metallic particles evolved from the electrodes from diffusing toinsulating cylindrical side wall member 31 to destroy the insulatingcharacteristic thereof. A (I-shaped dielectric trigger electrode 41 issupported upon a pair of trigger electrode support and lead'members 42and 43 which are passed through pinch 33 in base portion 32 of side wallmember 31. The open portion 44 of electrode 41 defining the trigger gapis aligned with an aperture 45 in shield member 40 to permit theinjection of a burst of conduction carriers into the vicinity ofbreakdown gap 37 when trigger electrode 41 is suitably pulsed. The edgesof trigger electrode 41 adjacent trigger gap 44 are coated with carbon,titanium or another gas-absorbing substance and impregnated with anionizable gas, as for example, hydrogen.

In operation, the device of FIG. 2 functions much the same as the deviceof FIG. 1. The voltage to be switched is connected between studs 46 and47 on electrode support members 38 and 39 respectively, and a source ofpulsed voltage is connected between dielectric trigger electrode supportand lead members 42 and 43. When it is desired to fire the device andrender the gap conducting, a pulse of, for example, 5-10 microseconds ofsignal voltage, which may range from -3000 volts, depending up on themagnitude of the voltage to be switched, is supplied thereto. abreakdown is initiated across trigger gap 44. This results in theevolution of i onizable gas from the adjacent portions of dielectrictrigger electrode 41 and, by virtue of the C-shaped configurationthereof, the injection of a burst of ionizable gas into breakdown gap 37to render the gap conducting.

While the invention has been set forth herein with re-. spect to certainspecific embodiments thereof many modifications and changes will readilyoccur to those skilled in the art. Accordingly, by the appended claims Iintend to cover all such modifications and changes as fall within thetrue spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric discharge device adapted to change from a non-conductingstate to a conducting state in response to a pulsed signal andcomprising: an hermetically sealed envelope evacuated to a pressure of10 mm. of mercury or less; a pair of primary electrodes located withinsaid envelope and spaced apart from each other to define a breakdown gaptherebetween; means for connecting said electrodes between terminals ofa voltage to be switched; a trigger electrode comprising a body of highdielectric constant having a gap therein and adapted to sustain atrigger discharge across said gap when a voltage is supplied thereto;and means for supplying pulsed voltage signals to said trigger electrodeto render said breakdown gap conducting.

2. An electnic discharge device adapted to change from a non-conductingstate to a conducting state in response to a pulsed signal andcomprising: an hermetically sealed envelope evacuated to a pressure of10-5 mm. of mercury or less; a pair of primary electrodes located withinsaid gap and spaced apart from each other to define a breakdown gapvtherebet-ween; means for connecting said electrodes between terminals ofa voltage to be switched; a trigger electrodecomprising a body of highdielectric constant having a gap therein; the dielectric constant ofsaid body being sufficiently high so that when a voltage is applied toportions of said body on opposite sides of said gap substantially all ofsaid voltage is developed across said gap to cause the initiation of atrigger discharge thereacross; and means for supplying pulsed voltagesignals to said trigger electrode to render said breakdown gapconducting.

3. The electric discharge device of claim 2 wherein said triggerelectrode body is formed of barium titanate. 4. An electric dischargedevice adapted to change from Upon application of this pulsed voltage,

'a non-conducting state to a conducting state in response to a pulsedsignal and comprising: an hermetically sealed envelope evacuated to apressure of 10* mm. of mercury or less; a pair of primary electrodeslocated within said envelope and spaced apart from each other to definea breakdown gap therebetween; means for connecting said electrodesbetween terminals of a voltage to be switched; a trigger electrodecomprising a body of high dielectric constant having a substantiallyC-shaped configuration and defining a trigger gap, the edges of saidbody adjacent said gap being coated with a material having goodgas-absorbing characteristics; means for supplying a pulsed voltagesignal to said trigger electrode to cause a trigger discharge to beinitiated across said trigger gap, resulting in the evolution ofionizable gas from the coating upon said body and the injection ofionized particles into said breakdown gap to render said gap conducting.

5. The electric discharge device of claim 4 wherein said coating of gasabsorbing material is charged with hydrogen gas.

6. An electric discharge device adapted to change from a non-conductingstate to a conducting state in response to a pulsed signal andcomprising: an hermetically sealed envelope evacuated to a pressure of10 mm. of mercury or less; an apentured first electrode and secondelectrode located within said envelope and spaced apart from each otherto define a breakdown gap therebetween; means for connecting saidelectrodes between terminals of a voltage to be switched; a triggerelectrode comprising a C shaped body of high dielectric constant havinga gap therein and adapted to sustain a trigger discharge across said gapwhen a voltage is supplied thereto, said trigger electrode being locatedso as to propel ionized conduction carriers through the aperture in saidfirst electrode and into said breakdown gap; and means for supplyingpulsed voltage signals to said trigger electrode to render saidbreakdown gap conducting.

7. An electric discharge device adapted to change from a non-conductingstate to a conducting state in response to a pulsed signal andcomprising: an hermetically sealed envelope evacuated to a pressure of10 mm. of mercury or less; a pair of primary electrodes located withinsaid envelope and spaced apart from each other to define a breakdown gaptherebetween, means for connecting said electrodes between terminals ofa voltage to be switched; a trigger electrode comprising a C-shaped bodyof high dielectric strength having a gap therein and adapted to sustaina trigger discharge across said gap when the voltage is suppliedthereto, said trigger electrode being laterally disposed adjacent saidbreakdown gap; and means for supplying pulsed voltage signals to saidtrigger electrode to render said breakdown gap conducting.

No references cited.

GEORGE N. WESTBY, Primary Examiner. JOHN W. HUCKERT, Examiner.

1. AN ELECTRIC DISCHARGE DEVICE ADAPTED TO CHANGE FROM A NON-CONDUCTING STATE TO A CONDUCTING STATE IN RESPONSE TO A PULSED SIGNAL AND COMPRISING: AN HERMETICALLY SEALED ENVELOPE EVACUATED TO A PRESSURE OF 10-5 MM. OF MERCURY OR LESS; A PAIR OF PRIMARY ELECTRODES LOCATED WITHIN SAID ENVELOPE AND SPACED APART FROM EACH OTHER TO DEFINE A BREAKDOWN GAP THEREBETWEEN; MEANS FOR CONNECTING SAID ELECTRODES BETWEEN TERMINALS OF A VOLTAGE TO BE SWITCHED; A TRIGGER ELECTRODE COMPRISING A BODY OF HIGH DIELECTRIC CONSTANT HAVING A GAP THEREIN AND ADAPTED TO SUSTAIN A TRIGGER DISCHARGE ACROSS SAID GAP WHEN A VOLTAGE IS SUPPLIED THERETO; AND MEANS FOR SUPPLYING PULSED VOLTAGE SIGNALS TO SAID TRIGGER ELECTRODE TO RENDER SAID BREAKDOWN GAP CONDUCTING. 